https://en.wikipedia.org/wiki/Life_imprisonment_in_Norway > The indeterminate penalty (civilian penal code), called "preventive detention" (Norwegian: forvaring), is set at up to 21 years' imprisonment, with no eligibility for parole for a time period not exceeding 14 years. If the prisoner is still considered dangerous after serving the original sentence, the detention can be extended by five years at a time. Renewal of the detention every five years can in theory result in actual life imprisonment.

So it can actually be longer.